CONDENSED CONSOLIDATED BALANCE SHEETS (Parentheticals) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Cash and cash equivalents	$ 259.0	$ 4,231.0
Accounts receivable, less bad debt reserve	1,091.0	1,190.0
Bad debt reserve	21.0	18.0
Prepaid expenses and other current assets	156.0	192.0
Regulatory assets	$ 2,194.0	$ 1,967.0
Preferred stock par value (in dollars per share)	$ 0.01
Cumulative preferred stock authorized (in shares)	20,000,000
Common stock par value (in dollars per share)	$ 0.01	$ 0.01
Common stock authorized (in shares)	1,000,000,000	1,000,000,000
Common stock outstanding (in shares)	502,235,354	501,197,784
Variable Interest Entity, Primary Beneficiary [Member]
Cash and cash equivalents	$ 224.0	$ 335.0
Accounts receivable, less bad debt reserve	48.0	56.0
Prepaid expenses and other current assets	19.0	34.0
Regulatory assets	821.0	1,059.0
Houston Electric [Member]
Cash and cash equivalents	228.0	335.0
Bad debt reserve	1.0	1.0
Prepaid expenses and other current assets	30.0	61.0
Regulatory assets	951.0	1,124.0
Houston Electric [Member] \| Variable Interest Entity, Primary Beneficiary [Member]
Cash and cash equivalents	224.0	335.0
Accounts receivable, less bad debt reserve	48.0	56.0
Prepaid expenses and other current assets	19.0	34.0
Regulatory assets	821.0	1,059.0
CERC Corp [Member]
Cash and cash equivalents	2.0	14.0
Accounts receivable, less bad debt reserve	428.0	894.0
Bad debt reserve	16.0	17.0
Prepaid expenses and other current assets	36.0	115.0
Regulatory assets	$ 189.0	$ 181.0
Cumulative Preferred Stock [Member]
Preferred stock par value (in dollars per share)	$ 0.01	$ 0.01
Cumulative preferred stock authorized (in shares)	20,000,000	20,000,000
Series A Preferred Stock [Member]
Preferred stock par value (in dollars per share)	$ 0.01	$ 0.01
Preferred stock aggregate liquidation preference	$ 800.0	$ 800.0
Preferred stock outstanding (in shares)	800,000	800,000
Series B Preferred Stock [Member]
Preferred stock par value (in dollars per share)	$ 0.01	$ 0.01
Preferred stock aggregate liquidation preference	$ 977.5	$ 977.5
Preferred stock outstanding (in shares)	977,500	977,500

Amount due from customers or clients, within one year of the balance sheet date (or the normal operating cycle, whichever is longer), for goods or services (including trade receivables) that have been delivered or sold in the normal course of business, reduced to the estimated net realizable fair value by an allowance established by the entity of the amount it deems uncertain of collection.

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